High-frequency filament-heating means



kJuly l0, l928.- 1,677,021

' w. E. DANLEY HIGH FREQUENCY FILANENT HEATING MEANS Filed oct. 6, 1927 3 Sheets-Sheet l July 10,1928. 1,677,021

` W. E.r DANLEY HIGH FREQUENCY FILAMENT HEATING MEANS Filed oct. e, 1927 :s sheets-sheet 2 r l r r W. E. DANLEY HIGH FREQUENCEv FILAMENT HEATING MEANS July 1o, 192s. 1,677,021

Filed oct. 6, 1927 s sheets-Sheet 3 45T l?! 4Q 45E www Marra/7 WARREN E. DANLEY, OF HIGHLAND f `Parental .nagI 1o. 192s.

UCTB COMPANY, INC., OF NORTH YORK. l

PARK, ILLINOIS,

CHICAGO, ILLINOIS, A CORPORATION OF NEW ASSIGNOR TO FAN STEEL PROD- HIGH-FREQUENCY FILAMEN T-HEATIN G MEANS.

Application led October 6,1927. Serial No. 224,328.

My invention relates to high frequency filament heating means and pertains more particularly to' the use of said means with f a radio receiver, this application being a continuation in part of my co-pending application, Serial No. 191,800, filed May 1G,v

1927. Heretofore attempts to use inaudible -frequency for heating the filaments of radio receiving sets have been unsatisfactory due to the instability of the set, to the tendency of the grids to swing positive and draw excessive current, to the fact that signal frequency builds/up regeneration in the succeeding Stages, to the fact that the oscillator tube may be damaged by excessive currents caused,

by improper manipulationof the set, to the fact that the high frequency current of the filament circuit tends to heterodyiie with an undesired signal, and to the fact that any ripple in the power vsource modulates the filament heating current to cause that ripple to become audible inthe loud speaker.

The object of this'invention is to overcome i these diflculties.

yments of the tliermionic tubes are directly -heated by a current of more than double'tlie highest frequency lof the signals to be received.

A further object is to eliminate all undesirable modulations of filament supply current by providing means for balancing irregularities in the plate .power supply of the high frequency generator (the oscillator tube) by introducing corresponding irregularities of properamplitude and phase in the grid circuit of said oscillator tube.

A further object of the. invention is toy provide a negative bias on the grid of the oscillator tube suflicient to prevent excessive plate current therein under any and all operating conditions.

A further object. is to rovide means to insure that the grids of tie tubes whose filaments are heated by this device will not swing positivel and draw current. Negative bias on the grid has hereto-fore been used (1) to restrict the plate. current of the tube to a desired value, (2) to operate the tube on a desired part of its characteristic curve, and (3) to provide against the grid of the A further object is to provide an improved radio receiving set combined with its power supply.

Other objects will be apparent as a detailed description of the invention proceeds.

A preferred embodiment of my invention is illustrated in 4the accompanying drawings, in which like parts aie represented b similar reference characters throughout t e several views.

l represents the schematic diagram of my improved radio receiver and power supply means.

Fig. 2 is a diagram showing the same power supply means, the drawing being simplified and parts omitted in order to show more clearly the oscillation generator.

Fig. 3 illustrates diagrainmatically a means for eliminatingA any ripple in the plate current supply of the oscillation generator.

Fig. 4 is a. detail showing the coupling of the. inductances in the oscillation generator.

Fig. 5 is a modilication showing the use of a signal frequency tiltering system in the iilament circuit of the radio receiver.

Figs. 6 and 7 are diagrammatic details of the fila-ment circuit explaining the action of the above filter system.

4The circuit illustrated in Fig. 1' includes an antennal 10, a six-stage receiver 11, a. B current supply 12, and an A current supply 13. The ground wire or zero potential conductor 14 connects the set to ground at 15. A conductor 16 connects conductor 14 to the negative side 27 of the B current supply. The antenna circuit is inductively connected to a convent-ional radio receiver illustrated as stages I, II, III, IV, V and VI. This receiver provides three stages of radio frequency amplification, a detector and .two stages of audio frequency amphtication. The radio frequency stages may be neutralized in any well-known manner, a c0nventional neutrodyne system being shown in the drawing. u

Power to operate this receiver' is furnished from the ordinary alternating current power mains through wires 17 to the primary winding 18 of a transformer. This transformer is provided with three secondary windings 19, 20 and 21. The terminals of secondary 19 are connected by conductors 22 to the filament of an oscillation generator 42. The terminals of secondary 20 are connected by conductors 23 to the plates of thermionic rectifier tubes 24. The filaments of these tubes are heated by current from secondary 21 supplied through conductors 25, as shown in the drawing. A conductor 26 connects the center of secondary 21 to choke-coil 28, the other terminal of which is connected to conductor 26 which is the positive side of the B current supply, and a conductor 27 taps the center of secondary 20 and leads to conductor 27 which is the negative side of the B current supply and which is connected to lground as above stated. On each side of the choke-coil 28 arc bridged filter condensers 29 and 30, which co-act with choke-coil 28 to smooth out the pulsations in the rectitied current.

Bridged across conductors 26 and 27 is a resistance 31. This resistance is tapped by a conductor 32 which leads to the plate circuit feed wire 33. The tap is made at a point which will give the desired plate voltage, which will necessarily depend on the receiving set used. A resistance 34, which serves to further reduce the voltage on the plate ot' the detector tube, is inserted between conductor 32 and conductor 35, which latter conducts the plate current for the detector tube. A condenser 36 is connected between conductors 35 and 27 and a condenser 37 is connected between conductors 35 and 26', their function being to cooperate with resistance 34 to more perfectly filter or smooth out the detector plate supply Voltage.

A negative bias resistance 38 is connected between the negative B current supply 27 and a conductor 39 leading to the center of the secondary 19. This resistance effects a negative bias on oscillator tube 42 and power amplifier tube VI. Its use in connection with tube 42 is shown in Figs. l and 3. The plate current flows from positive B (26') to the plate of the tube, through the tube to the filament and from the filament through 22. 39, and resistance 38 to negative B (27'). The IR drop across this resistance 38 obviously maintains the filament positive with respect to negative B, and since the grid is connected to negative B through 27" and 52, the filament is maintained positive with respect to the grid, or, in other words, the grid is negatively biased with respect to the filament.

rl`o operate cfiiciently, an oscillator tube rcquires a very high negative bias. It would he wasteful to secure all this bias by means of an IR drop across resistance 38. Accordingly grid condenser 43 and grid leak 44 are provided to give the major part of the required bias. But the condenser grid leak combination is effective to provide bias only when the tube is oscillating whereas resistance 38 provides a bias under all conditions of operation. The combination of these two methods is therefore an important feature, being economical of power' on the one hand, and on the other hand, providing against damage to the oscillator tube from the excessive plate current which would follow any cessation of oscillations if the grid leak condenser method were used alone.

A condenser' 40 is connected between conductors 27 and 39 in shunt with resistance 38 and a condenser 41 is connected between conductors 26 and 39. rl`he function of these condensers is clearly shown in Fig. 3. Since conductor 39 taps the center of secondary 19 which heats the filament of oscillator 42, it will at all times be at the mean potential. of said filament. The grid of oscillator tube. 42 is connected to 27', the negative side of the B current supply, through the grid condenser 43 in parallel with grid leak 44 and through 27 and 52. The plate of the oscillator tube is connected through 26 and 45 to the positive side of the B current supply 26.

While the voltage across 26 and 27 is substantially constant, there may be superimposed upon it a slight ripple due to the AC power source. Thus while the average value is V1, the maximum value will be V2 and the minimum value V3. When the voltage is increased as at V. the plate current is likewise increased, and when the plate voltage decreases the plate current is dccreased, thus causing a ripple in the current taken by the oscillator which necessarily modulates the high frequency oscillating current.

I If, however, the negative bias on the grid 1s increased by an amount equal to:

increase in plate voltwag, amplification constant of tube,

In the negative bias. 3k diagrammatically illustrates one methodk of accomplishing this fductance 45 to the positive B current supply 26 and the grid isconnected through grid condenser 43 in shunt with grid leak 44, conductor 27 and vinductance 52 to the 26', it being connectedfat the negative side of the B current supply 27',

as above stated. The inductance is inductively coupled with inductance 52 as shown kby Fig. 4, i. e., both inductances are wound on the same tube, and in the same'direction. A condenser 4,6 is connected between conductor 26" and theifeeder 47 of the filament sup ly circuit?. `Leading from feeder 47 are con uctors 48 to the respective filaments and each filament circuit also includes a condenser 49 and a conductor 50 leading from the condenser to conductor 14. A condenser 51 vis connected between the conductor 14 and the positive side of the B current supply opposite end of inductancev 45 from the connection of condenser 46 as shown in the drawing. ConrimarilyV to tune the osg primarily as blocking condensers; they form ow impedance paths forv `high frequency current but block direct current.

`A'resista'nce 53 is connected between feed wire 47 and conductor 14, its function being to provide negativebias for the grids of the tubesin stages I, II, III, andy V. Each grid is connected to conductor 14 by` conductor 50, as shown in -the`drawing, and since there is always a voltage drop vacross resistance 53, i due tothe flow of plate current through it,

the filalnent in each ,tube `(connected by conductor 48) will be maintained at a higher potential than the grid, or, in other words, the .grid kwill have l the necessary negative bias. This is most important in my circuit because additional ynegative bias is required, due to the ladditive effect of the filament power voltage, and the signal voltage, tending `to cause the grid to swing positive and draw current. Failure to supply this large negative bias for the grid may result in the failure of the set using high frequency current for filamentpower.

In order to prevent plate circuit interstage coupling inthe radio frequency stages, I have inserted in each stagea filter consisting of resistance 54 andfcondenserk 56. Resistance 54 i-s connected between the plate feed wire 33` and the conductor 55 and condenser 56 between conductor 55 and the filai ment of the tube. Resistance 54 forms a high impedance for signal frequencies and condenser 56 forms a low 1mpedance for said frequencies so that the signal tends to return through 56 to the filament circuit without traveling through 33, 32, 27', 16, 14 and 50, which might otherwise prove a troublesome common impedance. In the fourth stage (the detector circuit) I provide condenser 64 and condenser 65, as shown in the drawings. These condensers serve to bypass radio frequency and audio frequency, respectively, from the plate circuit off-the detector tube to the filament thereof.

The six-stage radio receiver shown is a conventional type and further description of it is not deemed necessary. The tube in the sixth stage operates the loud speaker and its filament is heated by current from secondary 19 through conductors 22. The

plate of this tube is connected by conductor 57 to a choke-coil 58, the other end of which is connected by conductor 59 to the positive side of. B current supply 26. Conductor 57 is also connected to condenser 60, the other side of which is connected by conductor 61 to loud speaker 62, which is connected by conductor 63 to the center of secondary 19.

The filament-s of the tubes in the receiving set are heated by an oscillating current set up in the circuit 45, 46, 47, 48,. 49, 50, 14 and 51. Sufficient energy is supplied by tube 42 to compensate for the energ lost in heating the filaments. The circuit 1s tuned by condenser 46 which is very small as compared tok condenser 51. The voltage drop across inductance 45 is equal to the voltage drop across condenser 46 added to that of the filament circuit and to that across condenser 51 and condensers in parallel therewith. Thus if the voltage drop across 45 were 400 volts, across 46 were 394 volts, and across 51 were 1 volt, the voltage drop across the filament circuit would be 5 volts.

Feed-back from one stage to a preceding stage may occur in the grid filament circuits and to avoid this, I may use separate filament heating circuits as shown in Fig. 5. To better understand the reason for this eX- pedient, reference is made to Figs. 6 and 7 in which I have schematically illustrated grid filament circuits of the first three stages ofl my receiver, as shown in Fig. 1. Assuming an amplification per stage of 10 and a signal voltage of unity on grid g1, the voltage on grid g2 would be 10 and on g, would lill ment is about 20 ohms and that of the connecting wires is negligible. Therefore, the current flowing from P8 may ow through filament f, to ground, but the resistance of this filament makes some of this current take the path 483, 47, 482 to P2 and 483, 47, 481 to P1, the voltages at points P3, P2 and P1 being approximately equal. At P2 and P, the current again divides, part flowing through filaments f, and f, and part through the paths c2', g2 and 0,', g1, respectively. Thus, instead of unity voltage at 9 there will be a greater voltage due to the high order of the voltage at g3, this constituting regenerative feed-back.

In the case of a receiver whose filaments are heated by radio frequency, the common methods of preventing or diminishing this feed-back (by-pass condensers across filaments, etc.) cannot be used. In Fig. 7 I haveschematically shown a method of cutting down this feed-back adapted for radio frequency filament heating means. I have, in effect, eliminated the common filament i feed wire 47 and have substituted a plu-- rality of tuning condensers 46,', 462', 46, for the single tuning condenser 46 of Figs. 1 and 6. Each of these condensers 46,', 46,. 46, will offer a very high im edance to the passage of current of signal requency. In other Words, instead of the direct path from P3 through 48 47 and 48l to P1, this current will have to travel through 483. 46,', 26, 46, and 48,' to P as shown in Fig. 7, impressing but slight volta e at P1.

The filtering effect of t e arrangement shown in Fig. 7 is of a higher order than ordinarily required. Usually a separation of the tubes into two groups, as shown in Fig. 5, is all that is necessary. It should be noted that when separate filament heating circuits are used, separate resistances 53 must also be used, as shown in Figs. and 7, the function of which is the same as above described with reference to Fig. 1.

From the above description, it will be a simple matter for anyone skilled in the art to construct a radio receiver and power supply therefor in accordance with my invention. For the six-stage set, three stages of radio frequency, a detector and two stages of audio frequency, I have found that the following values will give good results. Tubes in stages 1 to 5 are of the type known as 201A tubes, i. e.. they are the standard receiving tubes whose filaments require .25 amps. at 5 volts, whose detector plate voltage is usually 22.5 to 45 and which operate satisfactorily as amplifiers with a plate voltage of 135 and a negative grid bias of 9 volts Tube 42 and the tube instage VI are of the type known as 210 tubes; they use 7-71/ volts A. C. for heating filaments and their plates require about 400 volts D. C.

Tubes 24 are of the type known as 216B and they require 7 to 71A? volts A. C. and 550 volts (R. M. S.), respectively, on filaments and plates 115 volts A. C. across conductors 17 7.5 volts across the terminals of secondary 19 1100 volts across the terminals of 20 7.5 volts across the terminals of 21 100 henries1 for coil 28 (at 100 in. a. of pure 4.0 m. f. for condenser 29 8.0 m. f. for condenser 30 0.55 m. f. for condenser 41 1.0 1n. f. for condenser 40 4.0 1n. f. for condenser 36 0.1 m. f. for condenser 37 36,500 ohms for resistance 3l tapped to give 11,500 ohms from 26 to 32, and 25,000 ohms from 32 to 27 1,000,000 ohms for resistance 34 400 ohms for resistance 38 .01 m. f. for condenser 51 .00025 in. f. for condenser 46 .0001 m. f. and .00015 m. f. for condensers 46 and 46 of Fig. 5

11 turns (27 turns to inch) on 1% inch insulator tube for inductance 14 turns (27 turns per inch) on same tube for inductance 52 .002 m. f. for condenser 43 10,000 ohms for resistance 44 1 m. f. for condensers 49, 56, and 65 .002 m. f. for condenser 64 400 ohlns for resistance 53 800 ohms each for resistance 53 of Fig. 5

5000 ohms for resistance 54 Inductance 45 and capacity 46 (in series with 49 and 51, which have negligible tun ing effect), are so chosen as to satisfy the two following formulas, the first having to do with the fre uency of oscillation and the second with o taining maximum output from the oscillator tube.

1/L microhenry C mierofarad (2) C or L EiRLC where f is frequency in cycles C is capacity in farads L is inductance in henries In, is plate current in amperes EOD is plate voltage in volts RL is resistance in ohms ber of filaments is diminished the resistance.

RI, is increased and, from (2), if the oscillating circuit constants are unchanged, the

f power output of the oscillator tube will fall g tions in t y voltage.

off.v 'In other words, to an important extent, the power output will be automatlcally adjusted to the diminished load. Similarly, p whenL and C are proportioned to give maximum tube output for a. certain minimum plate voltafve, EDU, the efficiency of the oscillator will |fall ofi with any increase in the'plate For, from` (2) again, maximum tube output is obtained only with a certam ratio of plate voltage En, to plate current Iop and this ratio will vary as Eopns increased for, in a vacuum tube oscillator, plate current is proportioned not to plate voltage but to the sum: plate voltage plus amplification constant times grld voltage. Therefore, to an important extent the power output ma be made independent of fluctuae power ksupply voltage. Thus the automatic regulation referred to above l is obtained.

A feature of my` invention is the use of a frequency which prevents undesirable heterodyne effects. I have found that the use of a filament current fre uency, less than double the greatest signa fre uency for which the receiver is designed, wi l give said undesired heterodynes. For example, a filay ment current frequency of 30,000 cycles may heterodyne with a` signal frequency of 1,030,000 cycles to produce a beat of 1,000,000

cycles which would interfere with reception of a signal frequency of 1,000,000 cycles. At the other extreme, a filament currentfrequency of 1,990,000 cycles may heterodyne with a signal frequency of 990,000 to proi duce a beat of 1,000,000 cycles.

But if a filament current frequency of over 2,000,000 cycles is usedwith a receiver which will not handle a signal of over 1,000,000 cycles, no beat isp0ss`ible. I have also found that, due to the importance of stray capacity and resistance effects encountered in the use of ,high frequencies, it is desirable to avoid the use of any higher frequency than that necessary to meet the above requirement.

While I have described a. preferred embodiment of my invention, it is understood that I *amr not lilnited to the details set forth.

Any receiving circuit may be used in place of the neutrodyne set illustrated. Instead of the balancing condensers for eliminating the effect of ripple in the plate current supply of the oscillator tube, I mav employ other means for accomplishing this Iresult. For example, when the ripple in the plate voltage give a balancing effect, A ny is of the same frequency as the current for heating the filament ofthe oscillator, the grid return of the oscillator tube may be connected to the movable arm of a potentiometer whose terminals' are connected to the two filament leads, and so adjusted as to rectifier may be used' in place of the thermionic rectifier shown. A direct current source of pro r voltage may be used instead of alternating current with necessaryI changes in B supply circuit-s, etc.'

I have also found that approximately the same adjustment of the circuit constants as outlined above yields most satisfactory operation from the standpoint of elimination of audible disturbances traceable to fluctuations in the power source, for example, the hum tending to be present due to the commercial current power input.

It `will be notedl also that the term connected appears in certain of the claims.. Attention is directed to the fact that where the filament heating ,current is of high frequency, as in the present case, this term does not necessarily imply a conductive or galvanic connection, but includes also inductive or capacitive connection, since the high frequency current can readily pass through either a condenser or a transformer coupling in a circuit.

I do not limit myself to the wiring scheme, to values given in my preferred embodiment, nor to any other by the following claims:

1. In combination, a radio receiver including filament and plate circuits, an oscillation generator for generating currents of ultra audio frequency differing from the received signal frequency,

audio frequency oscillation generator for,

generating currents of ultra audio frequency details except as defined l connections for supplying power to saidplate circuit and to said gendiffering from ,the received signal frequency,

connect-ions for supplying power tosaid plate circuits and said generator, connections for supplying oscillating filament heating current from said generator to said filament circuits, and means for preventing modulation of the ultra audio frequency output'of the oscillation generator.

3. In combination, a radio receiver including a filament circuit, an ultra audio frequency oscillation generator comprising a thermionic valve having cathode, anode and control electrodes, connections between y the electrodes and a power source and to said' filament circuit, and means for inducing on the grid of said tube a change in the negative bias equivalent in effect to any chan e in anode voltage, whereby modulation o the said ultra audio frequency oscillations produced by the generator is prevented, and an unmodulated heating current is produced in said filament circuit.

4. In a combined power supply and radio receiver including their circuits, means for heating the filaments of the thermionic valves of the radio receiver by high frequency oscillating cui'- rent, and' mea-ns for suppl ing to the grid of cach valve a negative ias sufficient in magnitude to compensate for its tendency to swinv positive with respect to its filament due to flie additive effect of the filament and signal volta es.

5. In com ination, a multiple stage radio receiver, including tliermionic valves, and ultra audio frequency current, generator circuit for supplying heating current to the filaments of said thermionic valves, and means comprising series capacities in said circuit for isolating the separate stages of the receiver whereby regeneration of a signal and confequent oscillation are prevented.

6. In combination, an oscillation generator including a three electrode tube, a power source for said oscillation generator, means for eliminating ripple from power supplied to Said generator, a tlieriiiioiiic valve filanient circuit electrically connected to said generator whereby tlie oscillating current heats the filaments, and means for maintaining a negative bias on the oscillation generator tube whether the tube is oscillai ing or not.

7. In combination, a radio receiver including plate and filament circuits, an oscillation generator, means for supplying power to said generator and to said plate circuit, and means for supplying power from said generator to said filament circuit, said oscillation generator producing a current of a frequency more than double that of any signal frequency for which the receiver is dcsigned.

8. Means for stabilizin a multiple stage radio receiver using high requency A current supply which includes an impedance between the filament of one tube and the filament of another tube, said impedance serving tovprevent signal frequency feed back between grid filament circuits and also to tune an oscillating circuit in said A current supply.

9. In combination, a transformer provided with a. plurality of secondary windings, an oscillation generator, a rectifier, a filter circuit, connections from one secondary to the generator, other connections from said transformer through said rectifier and said filter to said generator, a plurality of thermionic valves having filaments, grids and plates. connections from said generator to said filaments, connections from said rectifier through said filter to said plates, and a resistance in the plate circuit return from the filaments to said rectifier connected to provide negative bias on the grids.

10. In a power supply unit, a transformer, a rectifier, a filter circuit, connections between them terminating in positive and negative direct current conductors, a resistance bridged across said conductors, an oscillation generator comprising a three electrode tliermioiiic tube, connections from said direct current conductors to said oscillation generator, connections from the terminals of a transformer secondary to the tube filament, a resistance between the center of said secondary and said negative direct current conductor, and impedance units bridged between said center and said positive and negative direct current conductors, respectively, whereby modulations of the plate current of the oscillator tube are prevented.

11. In combination, a multiple stage radio receiver including plate, grid and filament circuits, an oscillation generator including a three electrode thermionic tube, positive and negative connections for supplying B current to said plate circuits, an inductance in the plate circuit of the oscillator tube, condensers bridged from each side of said inductance to cach side of the receiver filament circuit, said condensers, inductance and receiver filament circuit forming the oscillating circuit of said oscillation generator, and connections from the grid circuits to the filament circuits comprising resistances and condensers bridged across said resistances.

12. In combination a radio receiver including plate and filament circuits, an oscillation generator, an oscillation circuit fed by said generator and connected with said filament circuit, said oscillation circuit being tuned to a frequency of more than double that of any signal frequency for which the receiver is designed.

13. In combination a radio receiver including plate and filament circuits, an oscillation generator, an oscillation circuit fed b v said generator and connected to said filament circuit. said oscillation circuit being tuned to a frequency immediately above the frequency double that of any signal for which the receiver is designed whereby heterodyne effects are avoided and power losses are maintained at a minimum.

14. In combination a radio receiver including a plurality of separated filament circuits, an oscillation generator, an oscillation circuit fed by said generator, said oscillation circuit being connected throu h impedance to said separated filament circuits respectively whereby the path of signal frequency current in the filament line is impeded.

15. In combination, an oscillation generator, a radio receiver including a filament circuit, connections for supplying energy to said generator including an inductance unit, capacity units connected from the terminals of said inductance unit to the opposite sides of the filament circuit, said capacity and inductance units being elements in an oscillat-ion circuit for supplying filament current at proper amperage and voltage to the tubes of the radio receiver.

16. The method of operating a thermionic valve having ay cathode and a controlelectrode which comprises heating the cathode kthereof by ultra audio frequency oscillating currentjand maintaining the control electrode thereof sufficiently negative with re- K10 circuits of saidvalves, said heating Currents being of a frequency differing from the sigy nal frequency, said `means including a thermionic generator tube, having an impedance in its grid circuit to maintain a negative bias while the tube isoscillating by virtue of the r'grid current,fand aseparate means for maintaining an independent negative bias on the kgrid 'whether the tube is oscillating or not.

18. In combination a multiple stage radio receiver including thermionic valves, an ultra audio frequency current source for heating the cathodes of said valves, a plu rality of cathode heating circuits. and means comprising series capacities to substantially isolate said circuits from one another With respect to signal frequency, whereby regeneration at signal frequency and consequent oscillation are prevented.

19. In combination a. radio receiver including a plurality of thermionic valves and their circuits, and a source of ultra audio frequency current connected with the cathode circuits of said valves, said source comprising an oscillation generator and an oscillation circuit, the constants of said oscillation circuit being so adjusted with respect to tlie load that the impedance in the work circuit of the oscillation generator is substantially resisted only and substantially equal to the internal resist-ance of said genciator whereby approximately maximum power output is obtained.

20. In combination, a radio receiver including a plurality of thermionic valves and their circuits, and a source of ultra audio frequency current connected with the cathode circuits of said valves, said source comprising an oscillation generator and an oscillation circuit, the constants of said oscillation circuit being so adjusted that any audible disturbances due to fluctuations in the power supplied to the source are minimized in the output of the radio receiver.

21. In combination, a radio receiver including a plurality of thermionic valves and their circuits, and a source of ultra audio frequency current connected with the cathode circuits of said valves, said source comprising an'oscillation generator and an oscillation circuit, the constants of said oscillation circuit being so chosen with respect to the load that the current supplied to the said cathode circuits is approximately proportioned to the load and for a given load is maintained substantially independent of variations of voltage supplied to the source.

In witness whereof, I hereunto subscribe my name this 30th day of September. 1927.

T/VARRIN E. DANLEY. 

